From the Advanced category, click on the General tab and make sure your browser defaults are properly set. Some malicious programs change browser start-up defaults without your knowledge so we recommend that you always check to see if Firefox is the default browser on startup. You should also submit crash reports to Mozilla to help fix crashes that may lead to securitiy problems. Mobile becomes a prime phishing attack vector, hackers will increasingly employ machine learning in attacks and cloud will increasingly be seen as fertile ground for compromise.
Source: https://threatpost.com/check-your-defaults/91737/